Punch stripper



H. M. MORAN PUNCH STRIPPER Jan. 28, 1941.

n Filed April 22, 1940 INVENTOR. f eer/1% Ma /9n,

Walcnied Jan. 28, 1941 PUNCH STRIPPER Harry M. Moran, Connersville, Ind., assignor to Iteady Machine Tool & Die 00. Inc., Connorsville, lnd., a corporation of Indiana Application April 22, 1940, Serial No. 330,847

12 Claims.

this invention relates to punch strippers, for stripping :lrorn punches the sheet material such as sheet metal which has been operated upon by the punch, to prevent such sheet material it irorn clinging to thepunch during its withdrawal. ln sheet-metal punching operations one or more punches are suitably mounted on a support so that they extend downwardly toward co-operating dies on a stationary support. The movable all support is then thrust downwardly to force the punches through the sheet metal supported over the dies. During the withdrawal oi thepunches the sheet metal tends to cling to the punches. T Lie conventional way of stripping the sheet ltt lllht' irorn the punches is to associate with the shes a stripper plate hung from the punch su port by stripper bolts and spring-pressed downwardly from the support. Such stripper pla e must have a plane lower surface for endug the sheet metal and must be provided l holes accurately alined with each punch. o avoid rnarring the surface of the sheet metal, it is usually necessary to provide the stripper I plate with a ground lower surface. In addition, the spring pressure on the stripper plate must be equalized. so that the stripper plate will tend to remain parallel to itself during its stripping operation. The provision of such stripper plates is a relatively extensive and difficult matter.

it is the object of my invention to eliminate the necessity for a stripper plate hung from the punclnsupport, by providing a stripping device which may be readily associated with each in-' dlvidual punch and supported thereby; and which til will be simple and effective, will have a longer lite than the conventional spring-pressed stripping plate, and will provide a stripping pressure which is applied directly to the area of use and which may be made greater than conveniently it possible with springs although it is often possible to secure improved stripping with my strippers with a decreased pressure.

in accomplishing these objects, I provide a rubber spool with a central longitudinal bore adapted to yieldingly grip and support itself on the shank of the punch, and I provide at that end oi such spool a bearing plate which will prevent scarring of the sheet-metal surface. Such a rubber stripper can be readily applied to each iiitill dividual punch and will support itself on the punch, so that the various machining operations and the expense and dlfliculty of providing a conventional stripper plate is eliminated.

The accompanylngdrawing illustrates my invention: In such drawing, Fig. 1 is a vertical sec tion through a punch and its associated die with suitable mountings and supports, and with a stripper embodying my invention in place on the punch; Fig. 2 is a section similar to Fig. 1 but showing the punch and the stripper in the positions they take at the end of the punching stroke; Fig. 3 is an isometric view of a stripper spool embodying my invention; Figs. 4, 5, and 6 are bottom plan views respectively of a round punch, a square punch, and an oblong punch, w each with an associated stripper embodying my invention.

The punch ill shown in the drawing is mounted in a suitable mounting block it and supported against a movable support It on the punch press. 13 Below the punch lll there is a die l3 supported in a mounting block it on a stationary support ill. The sheet inetal worlr it is shown in position resting on the upper end oi the die it.

This arrangement of punch and die and the lu l: associated mountings exemplifies a conventional arrangement.

Surrounding the punch i I] in Fig. l is a stripper embodying my invention. It consists of a rubber spool 20 with a central bore 2i oi the size adapted II to fit and grip the shank of a standard punch I0. The length of the spool is somewhat greater than the length of the punch it) which projects below the mounting block it, so that when the upper face of the stripper rests against the lower 3' face of the mounting block ii the lower end or the stripper is positioned below the lower end oi the punch. The lower end of the stripper carries a rigid annular bearing plate 22 suitably bonded to the rubber spool 20 and with a larger central 35 opening thanthe bore of the spool 2|], to readily pass the shank: oi the punch to into gripping erogagement with the walls of the bore. Preferably,

I provide bearing plates 22 at each end of the stripper so that it may be applied to the punch w either end up.

The rubber spool 20 is preferably barrel shaped as by being made in the form of a frustrated double cone with greatest wall thickness at its longitudinal center, for I have found that such a shape materially increases the stripping pressure and the life of the stripper, and the walls of the rubber spool are wholly unconfined. The bearing plates 22 should provide bearing surfaces which fit the surface of the sheet-metal work, and while 50 they will usually have plane bearing surfaces to fit the usual planar work, they may readily be shaped to fit work surfaces that are other than planar.

In the operation of the device, the punch sup- 55 port I2 is moved downwardly to carry the punch through a punching stroke and is then withdrawn. As the punch approaches the work it the bearing plate 22 first engages such sheet metal work I6, and upon further movement of the punch and its associated parts the rubber spool 20 is compressed longitudinally. This compression continues during the actual punching operation, and when the punch is withdrawn the compressed rubber spool 20 exerts a powerful downward force on the sheet metal work 16 to hold that work IS in place against the upper end of the die I3 and to strip it from the receding punch 10. This downward force exerted by the compressed rubber spool 20 is applied closely adjacent the edges of the opening from which the punch is being withdrawn. over the exact area where it is needed. When a number of punches are mounted upon a common support l2, individual stripper spools are respectively associated with the several punches. The stripper spools may be varied in size, to suit the size of the punch, and may thus exert ample force to strip the particular punch with which they are associated.

The material of the spools 2D, heretofore referred to as rubber, may be of any desired or suitable elastic material; such as natural rubher or any of the several synthetic rubbers available. In cross section, the bore of the rubber spool is concentric with the circumference thereof, so that substantially uniform pressure is exerted during the stripping action over the whole surface of the bearing plate 22. The length of the spool is sufficiently greater than the length of punch projecting below the face of the mounting block ii to provide for a suitable compression of the rubber of the spool during the punching operation, and the rubber thickness is suii'icient to give the necessary force. a

While the rubber spool itself, without the bearing plates 22, is operative to strip the punch, its use has been found to seriously mar the surface of the sheet metal work, in that it tends to bend the work down over the edges of the die. and to permit the edges of the punched hole to be drawn out of the plane of the work. which not only mars the work but causes such edges to pinch the punch so that the punch is injured and a greater stripping force is necessary. The use of rigid bearing plates 22 eliminates this dlfiiculty, especially if their bearing surfaces fit the work. Conveniently, I use steel washers for the bearing plates 20, and brass plate them to facilitate bonding them to the rubber.

Strippers embodying my invention may be used with punches of any cross-sectional shape. Thus, they may be used with the round punches shown in Figs. 1, 2, and 4, or square or oblong punches such as those shown in Figs. 5 and 6.

My strippers may be readily applied by simply slipping them over the shanks of the punches, where they will support themselves by yieldingly gripping the shanks of those punches. Their use eliminates the necessity for many machine operations and the accurate fitting which is necessary with the use of conventional springpressed stripper plates. Where a plate similar to 'a stripper plate may still be necessary, as is often the case with notching punches or edge trimming tools, its use may be greatly simplified by using my rubber strippers instead of springs, and mounting them on dowels on the punch support. In some such cases, the plate may be carried by the rubber strippers, as by providing the plate with dowels which enter gripping engagement with the lower ends of the rubber spools.

Moreover, I have found that the use of my rubber punch strippers has an advantageous effect upon the punching operation itself. Normally, the die with which the punch co-operates has an opening which is slightly larger than the punch itself, to provide clearance, and different clearances have been found necessary for use in punching sheet metal of difierent thicknesses. With my rubber strippers, I have found that the clearance may vary widely from that which is now considered essential, and that sheet-metal of widely differing thicknesses may be punched with the same punch and die set, so that it is possible to do a wide variety of work without the necessity of keeping on hand many die sets for the same hole-size and of changing die sets for the sole purpose of providing a clearance suitable for the thickness or character of the sheet metal work. The use of my rubber strippers also increases the life of the punch, for they not only permit the use of a greater clearance which in itself reduces the work imposed upon the punch, but they firmly hold the edges of the punched holes against bending to a position in which they pinch the punch, so that they decrease the wear on the sides of the punch.

I claim as my invention:

1. A punch-stripper, comprising a barrelshaped spool having a body of rubber-like elastic material with a longitudinal bore adapted to yieldingly grip the shank of a punch, and an annular bearing plate carried thereby at its lower end, said stripper being of a greater length than the length of punch projecting from its holder.

2. A punch-stripper, comprising a barrelshaped spool having a body of rubber-like elastic material with a longitudinal bore adapted to yieldingly grip the shank of a punch, and a rigid annular bearing plate carried thereby at its lower end, said stripper being of a greater length than the length of punch projecting from its holder.

3. A punch-stripper, comprising a barrelshaped spool having a body of rubber-like elastic material with a longitudinal bore adapted to yieldingly grip the shank of a punch, and annular bearing plates carried by the ends thereof, said stripper being of a greater length than the length of punch projecting from its holder.

4. A punch-stripper, comprising a rubber-like elastic body with a longitudinal bore adapted to a support itself upon a shank of a punch by frictional engagement between .the walls of the bore and the surface of such shank, and an annular bearing plate carried thereby at its lower end.

5. A punch-stripper, comprising a rubber-like elastic body,with a longitudinal bore adapted to support itself upon a shank of a punch by frictional engagement between the walls of the bore and the surface of such shank, and a rigid annular bearing plate carried thereby at its lower end.

6. A punch-stripper, comprising a rubber-like elastic body with a longitudinal bore adapted to yieldingly grip the shank of a punch, and annular bearing plates carried by the ends thereof.

'7. A punch-stripper, comprising a rubber-like elastic body with a. longitudinal bore adapted to yieldingly grip the shank of a punch, and rigid bearing plates carried by said body at its ends and having holes alined with said bore and Sufflciently larger than the bore to pass such punchshank.

8. A punch-stripper; comprising a barrelshaped spool having a body of rubber-like elastic material of annular cross section with a greater diameter at the center of the spool than at its ends, said spool having a longitudinal bore adapted to grip a depending shank and support the spool thereon, and bearing plates carried by the ends of thespool.

9. A pressure element for a punch stripper,

comprising a rubber-like elastic body of annular cross-section and of a wall thickness greatest at its longitudinal center and decreasing toward its ends, said element being adapted to support itself in use by gripping engagement with a de-, pending member received in its central opening.

10. In a sheet-metal punching device, having a stationary support, a die supported thereon, a movable support adapted to be moved toward the stationary support, anda punch element mount- 1 ed on said movable support in position to cooperate with said die, a1punch stripper comprising a rubber-like elastic body having a central bore carriedby said punch and supported thereonby gripping engagement of the elastic walls of said bore on the punch, and a rigid bearing plate carried by said elastic body with its bearing face below the lower end of said punch, said bearing plate having an opening positioned to pass said I much.

be pressed against said press it during a downward stroke of the mov- 11. In a sheet-metal punching device, having a stationary support, a die supported thereon, a movable support adapted to be moved toward the stationary support and carryinga punch element in position to co-operate with said die and providing a depending shank, a punch stripper comprising a rubber-like elastic body having a central bore supported from said movable support by frictional engagement of the walls of the bore on said shank, and a rigid bearing plate carried by said elastic body withits bearing face below the lower end of said punch.

12. In a sheet-metal punching device, having a pair of relatively movable supports, a die and an operating element respectively mounted on said supports in position to co-operate with each other, a stripper for said operating element, comprising a barrebshaped rubber-like elastic element havirfi a central bore, and supported on said movable support by gripping engagement with a depending shank received in its bore, and a bearing plate carried by said elastic element with its bearing face below the end of said operating element, said plate being adaptedto elastic element to comable support and to be pressed downwardly by said elastic element during the return stroke to strip said operating element.

HARRY M. MORAN. 

